Liquid crystal display devices are used across a wide range of industries and, taking advantage of their thinness, low power consumption, etc., are increasingly applied to mobile terminals (portable devices) such as cell-phones and tablet PCs.
Backlights used in liquid crystal display devices consist of a light source, a light guide plate, and an optical sheet, which are generally held integrally by resin molded frame. Convex protrusions are then provided at several points on the periphery of the optical sheet in a manner fittable into concave fitted portions provided in the frame to prevent the optical sheet from being displaced when an external force is applied thereto.